At present, "capacity" is the prevailing paradigm for covert channels. With respect to steganography, however, capacity is at best insufficient, In this paper, we propose a new paradigm called "capability" which gauges the effectiveness of a steganographic method. It includes payload carrying ability, detectability, and robustness We also discuss the use of zero-error capacity for channel analysis and demonstrate that a JPEG compressed image always has the potential to carry hidden information.